Staphylococci cause a wide spectrum of infectious diseases spanning from rather minor skin infections to serious conditions such as sepsis, pneumonia and endocarditis. Although Staphylococcus aureus is by far the most virulent of species, Staphylococcus epidermidis and Staphylococcus lugdunensis have also been found to cause severe infections mostly in immunocompromised individuals. In the past, highly virulent S. aureus strains were confined to the hospital environment mostly affecting immunocompromised patients or individuals with underlying co-morbidities. Unfortunately, similar strains have recently emerged in the community causing severe infections in otherwise healthy individuals. To a lesser extent and slightly different pathology, Staphylococcus epidermidis and Staphylococcus lugdunensis seem to follow the same pattern. Most of these strains have evolved to be resistant to antibiotics, which resulted in a worldwide epidemic and an enormous burden for the healthcare system. Therefore, the necessity of a vaccine or identification of novel or alternative therapies for the treatment of these infections has become an unmet and pressing medical need. Despite intense efforts, the molecular mechanism of staphylococcal infections is incompletely understood, but it seemingly involves a large number of virulence factors such as adhesins, toxins and immunomodulators. To date, adhesion to host tissues is considered the foremost stage of infection and plays a vital role in the survival of the invading organism. Most likely, the synthesis of toxins and immunomodulators plays a role later in the disease process and depends on the first step of infection. Hence, proteins responsible for adherence have long been recognized as targets for drug and vaccine development. In staphylococci, as well as other Gram-positive bacteria, adhesion to host tissues is mostly mediated by a family of cell-wall-anchored (CWA) proteins referred to us microbial surface components recognizing adhesive matrix molecules (MSCRAMMs). These proteins have been shown to a) mediate adherence to host proteins, b) participate in self-aggregation and c) modulate the biology of the ligand protein. Furthermore, MSCRAMMs have been shown to be virulence factors in animal models of infection since a mutant lacking all these molecules fails to cause disease. Vaccination with recombinant MSCRAMMs or inhibition of their functions resulted in significant protection against disease. Based on these observations, it is widely agreed that identification of ligands for MSCRAMMs would contribute to a better understanding of molecular events leading to infection and would help us design effective vaccine or targeted therapeutics for disease prevention and treatment. To that end, this proposed research aims to establish a high-throughput phage display methodology to identify ligands for MSCRAMMs. This work will also serve as a feasibility study to determine if this technique is suitable for large-scale ligand discovery for bacterial cell surface proteins. PUBLIC HEALTH RELEVANCE: Staphylococcus aureus is the leading cause of bloodstream, lower respiratory tract, skin and soft tissue infections in the United States with an annual mortality approaching 100,000 Americans lives. Our research aims to better understand staphylococcal infection and to set the grounds for targeted therapies against this disease.